#box {
    width: 300px;
    height: 500px;
    border: solid 1px black;
}

#box .cont {
    height: 379px;
    overflow: auto;
    padding: 10px;
}

#box .cont::-webkit-scrollbar {
    display: none;
}

.cont p {
    max-width: 250px;
    word-wrap: break-word;
    border-radius: 10px;
    padding: 5px;
    margin: 5px;
    clear: both;
}

.cont p:nth-child(2n) {
    background: rgb(80, 211, 80);
    float: left;
}

.cont p:nth-child(2n-1) {
    background: rgb(115, 227, 231);
    float: right;
}

#box form {
    border-top: 1px solid black;
    height: 100px;
    display: flex;
}

form * {
    margin: 0;
    padding: 0;
    border: none;
    background-color: none;
    height: 100px;
    outline: none;
}

#txt {
    width: 220px;
    padding: 10px;
    height: 80px;
}

#btn {
    width: 60px;
    border-left: 1px solid black;
}